The field of art to which this invention is directed is catalysts for the hydrogenation of aromatic compounds.
Nickel catalysts have been widely used to catalyze the hydrogenation of aromatic compounds.
U.S. Pat. No. 3,461,181 discloses a process for hydrogenating aromatic compounds using a catalyst containing 2-60 percent nickel, 2-80 percent sodium or alkaline earth fluoride and 12-96 percent silica or alumina.
Catalysts for the hydrogenation of benzene are disclosed in U S. Pat. No. 3,622,645. These catalysts, which are comprised of 5 to 90 percent nickel on kiselguhr, have particle sizes of not more than one-tenth inch in diameter.
Nickel or cobalt on silica catalysts for the hydrogenation of aromatic compounds are described in U.S. Pat. No. 3,661,798. Such catalysts, when deactivated by sulfur, can be regenerated by heating the catalyst in the presence of oxygen followed by contacting the catalyst with liquid water and then hydrogen.
A process for hydrogenating aromatic compounds using nickel/silica catalysts, wherein the nickel surface area is greater than 70 m.sup.2 /gm of catalyst and the sodium content is less than 0.2 weight percent, is described in U.S. Pat. Nos. 3,859,370 and 3,868,332.
The hydrogenation of aromatic compounds using sodium borohydride reduced nickel supported catalysts is described in U.S. Pat. No. 3,869,521.
Nickel-alumina catalysts having a high degree of thermal stability are described in U.S. Pat. No. 4,042,532.
Highly active hydrogenation catalysts made with nickel on a refractory oxide are described in U.S. Pat. No. 4,160,745.
Nickel on gamma-alumina catalysts are disclosed in U.S. Pat. No. 4,490,480. These catalysts have a nickel surface area of between 80 and 300 m.sup.2 /gm of reduced nickel in the catalyst wherein the nickel crystallites have an average diameter of 10 to 50 angstroms.
In Canadian Patent No. 1,080,685, hydrogenation catalysts are described which are comprised of, for example, 45 percent nickel, 5 percent copper and 50 percent silica having a nickel surface area of 50 to 100 m.sup.2 /gm of catalyst and a total surface area of 150 to 300 m.sup.2 /gm.
In Netherlands Patent application 67 14,401, hydrogenation catalysts are prepared by mixing a nickel or cobalt salt solution with a stabilized silica sol, precipitating a composite by adding base, filtering, drying, calcining and treating with hydrogen in situ at 300.degree. C.
Catalysts for the hydrogenation of alkyl benzenes are disclosed in Netherlands Patent Application 6,913,613. Nickel nitrate is precipitated onto aerosil using urea, followed by calcination and reduction at 450.degree. C. The catalysts have a nickel crystallite size of 50 angstroms.
One of the problems that arises in the hydrogenation of aromatic hydrocarbon feedstocks is rapid catalyst deactivation due to poisoning by sulfur compounds in the feedstock. The problem is very pronounced in the hydrogenation of aromatic hydrocarbons in heavy or high boiling hydrocarbon fractions which contain large organosulfur molecules, such as benzothiophene and dibenzothiophene. Such large sulfur containing molecules can block the pores in the catalyst resulting in rapid loss of catalyst activity.
A good hydrogenation catalyst should be reasonably sulfur resistant so that it will be able to maintain good hydrogenation activity for an extended period of time when used in reactions involving sulfur-containing feedstocks. The catalyst must be effective in picking up sulfur so that the inlet portion of the catalyst bed can act as a guard to provide protection to the remaining catalyst bed to obtain longer overall catalyst life.
A highly active catalyst should be in the form of small extrusions or certain specifically designed shapes with high outer geometrical surface area. The nickel content of the catalyst should be relatively high for the hydrogenation of aromatics in heavy hydrocarbon feedstocks so as to have the maximum possible nickel surface area for extra sulfur resistance.
An ideal catalyst for the hydrogenation of heavy feedstocks not only should have a high nickel surface area but should have a proper distribution of macro, meso and micropores for optimum porosity as well as good catalyst crush strength.